Picking a welding gas cylinder sounds simple until you start looking at the different sizes.
Go too small and you will spend more time than you would like getting refills. Go too big and you have a heavy cylinder taking up space that you may not need.
For most home MIG and TIG welders, 40, 80, and 125 cubic foot (“cf”) cylinders are the sizes you are most likely to come across.
So, let’s look at how big they are, how long the gas lasts, and which size makes the most sense for you.
Common Welding Gas Cylinder Sizes for MIG & TIG
There are plenty of welding gas cylinder sizes on the market. But for a homeowner or hobby welder, the three most common sizes you are likely to consider are 40, 80, and 125 cubic feet.
For MIG welding mild steel, these are commonly filled with a 75% Argon and 25% CO2 mixture, often called C25.
For TIG welding, 100% Argon is the usual choice for general welding. Pure Argon is also commonly used for MIG welding aluminum.
But that does not automatically make it the right one for everyone:
- A 40 cf cylinder is much easier to carry around.
- An 80 cf cylinder sits nicely in the middle.
- A 125 cf cylinder is a good choice if it mostly lives in your shop and you want fewer trips for refills.
Here is a quick way to look at it:
What Tank Size Do You Actually Need?
| Tank Size | Best Suited For | Main Consideration |
|---|---|---|
| 40 cf | Occasional or portable welding | Easier to move, but more frequent refills |
| 80 cf | Regular DIY and hobby welding | Good balance of size and capacity |
| 125 cf | Frequent home or workshop welding | Longer between refills, but heavier |
Refills are another thing worth thinking about.
Larger cylinders often cost less per cubic foot of gas to refill. So, if you have the room and weld regularly, moving up one size can make sense.
But check what your local gas supplier stocks before buying anything.
That little phone call can save you some grief later. Cylinder sizes and exchange policies vary between suppliers, and there is no point finding a bargain online only to discover nobody locally wants to refill it.
Welding Gas Cylinder Dimensions & Weight
Cylinder dimensions are not completely standardized.
Two tanks with roughly the same gas capacity can have slightly different dimensions and weights depending on the manufacturer.
The figures below are typical examples rather than dimensions that apply to every cylinder.
| Size | 40 cf | 80 cf | 125 cf |
|---|---|---|---|
| Approx. Height | 18 to 23 in. | 31 to 36 in. | 42 to 48 in. |
| Approx. Diameter | 6½ to 7 in. | Around 7 in. | Around 7 to 7¼ in. |
| Approx. Empty Weight | 22 to 24 lbs | 39 to 47 lbs | 51 to 65 lbs |
| Typical Service Pressure | 2015 PSI | 2015 PSI | 2265 PSI |
Again, these measurements vary.
If you are trying to squeeze a cylinder into a welding cart, cabinet, truck, or a particular corner of your shop, check the dimensions of the actual cylinder before ordering it.
It is also worth knowing that welding cylinders are sometimes identified using letters or numbers.
The problem is that these names are not universal.
One supplier’s letter designation does not necessarily match another supplier’s cylinder, so cubic-foot capacity and physical dimensions are much more useful when comparing them.
Your local gas supplier can also tell you which sizes are popular in your area and, more importantly, which customer-owned cylinders they will refill or exchange.
There is a myth that you can only buy empty tanks online. But that is just wrong.
Full Argon and Argon/CO2 cylinders are sold online as well. Just check that your local supplier will refill or exchange the cylinder before you buy it.
Recommended Argon/CO2 Tank Sizes for MIG
75% Argon and 25% CO2 is one of the most commonly used shielding gas mixtures for MIG welding mild steel.
Related read: MIG Welding with 100% Argon Shielding Gas
Recommended 100% Argon Tank Sizes for TIG
100% Argon is the normal choice for most TIG welding. It is also commonly used for MIG welding aluminum.
Do not use a 75/25 Argon/CO2 MIG mixture for TIG. The CO2 is an active gas and will cause problems with the tungsten and weld.
How Long Will MIG/TIG Welding Gas Last?
How long a cylinder lasts mainly depends on your gas flow rate.
For MIG welding mild steel, around 20 to 25 cubic feet per hour (“cfh”) is a common starting point.
For TIG welding, around 15 to 20 cfh is more typical.
These are not magic numbers.
The exact setting depends on things like the nozzle or cup size, welding position, torch setup, and air movement around the weld.
To calculate the approximate gas-flow time:
Gas flow time (hours) = cylinder volume (cf) / gas flow rate (cfh)
For example, take an 80 cf cylinder running at 20 cfh:
80 cf / 20 cfh = 4 hours
That means roughly four hours of continuous gas flow, not four hours spent in your workshop.
Unless you are laying one enormous weld, plenty of your time will be spent positioning parts, cleaning metal, grinding, and doing everything else that happens between welds.
Related read: MIG Welder Gas Regulator Settings
Welding Gas Cylinder Runtime Chart
Here is the theoretical gas-flow time for the three cylinder sizes at different flow rates:
| Flow Rate | 40 cf | 80 cf | 125 cf |
|---|---|---|---|
| 10 cfh | 4.0 hrs | 8.0 hrs | 12.5 hrs |
| 15 cfh | 2.7 hrs | 5.3 hrs | 8.3 hrs |
| 20 cfh | 2.0 hrs | 4.0 hrs | 6.3 hrs |
| 25 cfh | 1.6 hrs | 3.2 hrs | 5.0 hrs |
| 30 cfh | 1.3 hrs | 2.7 hrs | 4.2 hrs |
| 40 cfh | 1.0 hr | 2.0 hrs | 3.1 hrs |
These are theoretical figures, so your actual use will be a little different.
Purging the line, checking your flow rate, small leaks, and TIG pre-flow and post-flow will all use additional gas.
Tip: One habit you may want to adopt is backing off the regulator when you finish for the day.
Close the cylinder valve, release the pressure from the regulator, then back the adjusting knob out until the spring pressure is removed.
Apart from taking the load off the regulator, it forces you to check and set your gas flow again next time you weld. That is not a bad habit to have.
100% CO2 Cylinders for MIG Welding
While it is not for everyone, you can use pure CO2 for MIG welding steel.
CO2 is plain-old carbon dioxide. It is the same stuff used in fire extinguishers and to put the fizz in beer and soda.
The main attraction is cost. Straight CO2 is generally cheaper than an Argon/CO2 mixture and gives good penetration, although the arc is harsher and you normally get more spatter.
There are two important differences when buying a CO2 cylinder:
- CO2 cylinders are normally rated by the weight of CO2 they hold rather than cubic feet.
- CO2 normally uses a different cylinder connection from Argon and Argon/CO2 mixtures.
In the US, Argon and common Argon/CO2 welding mixtures normally use CGA-580. Pure CO2 normally uses CGA-320.
So, do not expect your normal Argon regulator to simply screw onto a CO2 cylinder.
Also read: What is the Best Gas for MIG Welding?
CO2 Cylinder Sizes and Runtime
One pound of CO2 gives roughly 8.7 cubic feet of gas.
At around 20 cfh:
| CO2 Size | Approx. Gas Volume | Approx. Flow Time |
|---|---|---|
| 1¼ lbs | 11 cf | ½ hr |
| 5 lbs | 44 cf | 2¼ hrs |
| 10 lbs | 87 cf | 4½ hrs |
| 20 lbs | 175 cf | 8¾ hrs |
| 50 lbs | 437 cf | 22 hrs |
Again, these are continuous gas-flow times rather than actual time spent working.
How to Tell How Much Welding Gas Is Left
With Argon and Argon/CO2 mixtures, the high-pressure gauge gives you a reasonable idea of how much gas remains.
If a cylinder reads around 2,000 PSI when full and later reads around 1,000 PSI at a similar temperature, it has roughly half of its usable gas remaining.
But do not treat the gauge like a precision fuel gauge.
Pressure changes with temperature, and different cylinders can have different service pressures.
As a general rule, learn what your cylinder reads when freshly filled and use that as your reference.
CO2 Is Different
You cannot judge the amount of CO2 left in the same way.
CO2 is stored largely as a liquid. While liquid remains in the cylinder, pressure is affected more by temperature than by how full the cylinder is.
The easiest way to find out how much is left is to weigh it.
The empty or “tare” weight should be stamped on the cylinder. Subtract this from its current weight and you have a good idea of how many pounds of CO2 remain.
Simple, and much more useful than staring at the pressure gauge hoping it will tell you.
Buying and Using a Welding Gas Cylinder
Before buying a cylinder, work out where you are going to get it filled.
Some suppliers refill customer-owned cylinders while others exchange them. Some also limit the sizes or types they will accept.
This matters even more if you are buying used. A cheap cylinder is not much of a bargain if your local supplier will not touch it.
A few other things are worth remembering:
- Argon and Argon/CO2 cylinders normally use CGA-580 connections in the US.
- Pure CO2 normally uses CGA-320.
- Keep cylinders secured so they cannot fall over.
- Close the cylinder valve when you finish welding.
- Fit the valve protection cap when moving a cylinder where applicable.
- Do not move a cylinder around by grabbing the regulator or valve.
There is a lot of pressure sitting inside one of these tanks, so treating it with a little respect is worthwhile.
What Size Welding Gas Cylinder Should I Buy?
For occasional welding or if you need something easy to move, a 40 cf cylinder can work fine.
For most home and hobby welders, an 80 cf cylinder gives a good balance between portability and capacity.
If you weld regularly and the cylinder mostly stays in your shop, a 125 cf cylinder gives you considerably more welding time between refills.
Before buying, ask yourself three things:
- How much welding do I actually do?
- Where am I going to keep the cylinder?
- Can my local supplier refill or exchange it?
Answer those and choosing between a 40, 80, or 125 cf cylinder becomes much easier.
Related:
What gas is used for welding? – Different types & Uses
Welding Gas Prices – How Much & Where to Buy